3-difluoromethyl-1-methyl-pyrazol-4--1h- carboxylic acid alkyl esters and the like

The present disclosure provides 1-methyl -1H- carboxylic acid alkyl ester and analogs thereof pyrazol-4-one 3 for preparing difluoromethyl. Reaction process comprising the Claisen condensation method, in which the enolate was acidified after removal of the remaining starting material and byproducts (e.g., excess ethanol and ethyl acetate). The method further comprises by reacting a trialkyl orthoformate ester by reacting with the residual water is completely dried difluoroacetoacetate acetic acid alkyl esters and the like prior to use in the next step. The method includes the use of Na2CO3 and / or K2CO3 to promote cyclization reaction to yield 3-difluoromethyl-1-methyl -1H- pyrazole-4-carboxylic acid alkyl ester. I.e., the method further comprises 3-difluoromethyl-2-methyl -1H- pyrazole-4-carboxylic acid group is effectively removed by the formation of positional isomers as a byproduct precipitated in the closed-loop mixed solvent system ester, thus eliminating the need for recrystallization of the final product.